NOTES
ting the ratio of abkorbance'of fraction'45 (relatively pure protein) to that of various non-protein fractions at a range of wavelei-@hs (Fig. 2) it is evident that, in the region 220 to 225 rnp, absorbance due to protein reaches a maximum relative to absorbance due to contaminants. Absorbance in this region should therefore be reasonably specific for protein and also be very sensitive.
TOMBS et aZ.l, in recommending spectrophotometric determination of serum protein at 210 mE_c as an extremely sensitive procedure, pointed out that absorbance in this region is largely due to the peptide bond. Consequently, proteins from different sources have similar absorption coefficients at this wavelength. Instrumental limitations to analysis at these wavelengths have been discussed by SAIDEL eE ad.0 and TOMBS et nL.1 The use. of this procedure places certain restrictions on the choice of buffers. The strong absorbance of succinate, phthalate and barbiturate makes estimations at 220 mp difficult in their presence. Sodium hydroxide, acetate, glycine and Tris can be used at a concentration of 0.01 M and sodium chloride, cacodylate, borate, phosphate 'and ammonium sulphate are satisfactory up to and above 0.1 *AI. The absorbance of protein at 220 mp accords with Beer's Law up to 2.0 and is virtually independent of p,M between values of 3. and II.